The project has two objectives. (1) We are documenting normal prenatal craniofacial morphogenesis in M. mulatta by a combination of photographic, radiologic, and histologic techniques. (2) We are investigating possible teratogenic effects of polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). PCBs, a stable series of chemicals widely used in industry, have become environmental pollutants of proven toxicity. Experimentally they have caused aberrant amelogenesis and dental follicle formation in young rhesus monkeys. TCDD is a contaminant in industrial compounds such as pentachlorophenol and the herbicide 2,4,5-T. It is a known teratogen for rodents, inducing cleft palate among other malformations, and has been implicated in stillbirths and human birth defects following the use of defoliants in Vietnam. Both compounds have proven to be potent abortifacients when administered orally during weeks 4 to 6 of pregnancy at doses of 1 or 5 micron g/kg for TCDD, and 0.6 or 3 mg/kg for 3,4,3',4'-tetrachlorobiphenyl. Fetuses which were not aborted at 0.2 or 1 micron g/kg TCDD showed abnormalities in the uvula and soft palate and in tooth formation.